Installation of two GFCIs (Ground Fault Circuit Interrupter) on the same circuit.
This post shows how I installed two GFCIs on the same circuit correctly without sharing a common neutral or "daisy chaining" them.
(I am not a professional electrician, just a DIYer with some electrical experience, call a professional electrician if you are in doubt about any of this).
Initially, I had installed a single GFCI outlet near the beginning of one of our larger home circuits in an effort to save time and money. I really only needed the GFCI to protect three outdoor outlets: Two in the garage and one on the back porch. Because my first garage outlet was near the beginning of the circuit and my back porch outlet was at the very end, I installed a single GFCI in the garage to protect all three outdoor outlets as shown here in a simplified version.
My Original Circuit Wired with One GFCI Protecting Everything
(Caused me occasional nuisance trips)
My newly bought GFCI was manufactured with the Line side on the top terminals which I have depicted in my diagram. This makes more sense to me logically to install the top Line wires first and then bottom Load wires next. Having the Line side on the top terminals seems to help emphasize the idea of the Load side being downstream in the circuit. The older GFCIs that I installed 10 years ago came with the Load side on top.
If you are lucky, a single GFCI outlet can be installed to protect many outlets downstream. The problem is that a GFCI outlet is very sensitive and the more outlets it protects, the more likely you are to leave something permanently plugged in that will cause some nuisance tripping. My problem may have come from the fact that this one GFCI was actually protecting 15 different outlets or wired items.
Every two to six weeks the GFCI would trip shutting down all fifteen of these items at various times of day seemingly independent of what was powered by the circuit at the time. That frequency was seldom enough to make it nearly impossible to identify the source of the current leak.
To make matters worse, the outlet would trip leaving my family occasionally locked out of the house because it fed power to our garage door opener. I suspect that the problem may have been one or more of these possibilities:
1. The battery charger on our older laptop
2. A dirty potentiometer in an older piece of equipment on our stereo
3. The wiring inside GFCI box such as a side terminal too close to the grounded box (likely)
4. A faulty GFCI (rare)
I finally gave in and rewired the circuit with two new GFCIs such that all the outlets and lighting in between that did not need to be protected by a GFCI were left out of the downstream portion of the first GFCI in the garage. This solution addressed all of the four possibilities listed above.
Circuit Wired with Two Isolated GFCIs
I added a pigtail splice and wire nut for the hot and neutral sources so that the Line side could be split.
Note: The pigtail splices and wire nuts are not necessary in this particular situation and could have been left out by simply connecting the hot and neutral from the right branch of the circuit above to the extra Line terminals of the first GFCI (The hot and neutral circuit nodes can exist at the Line terminals of the GFCI or at the pigtail splices). The pigtail splices make the diagram look a little more clean and easy to read and would need to be in place if there were another Load branch in the circuit that needed to be isolated from the GFCI.
This circuit wired without pigtail splices using the duplex Line terminals
You will notice that the garage door opener is still on the Load side of a GFCI protected circuit branch, but it is now grouped together with only a few other items. The garage door opener is plugged into an oulet in the ceiling of the garage which is subject to a great deal of humidity and moisture, so I chose to leave it on the Load side of the first GFCI. Had I chosen to exclude it, I would simply have disconnected the hot and neutral wires from the Load side of the GFCI and joined the opener's wires to the appropriate pigtail splice at the top.
The circuit wired so that the GFCI does not protect any outlets downstream
If I continue to have occasional nuisance trips on the circuit, I will wire as shown above. The pigtail splices are already in place if this becomes necessary.
The remaining pictures show how I installed the new garage GFCI in place of an existing GFCI outlet. Originally there was a simple duplex outlet at this box, so I will mention how I found the Line side and Load sides of the circuit when I initially wired the old GFCI.
Don't forget to turn off the breaker to the circuit you are working on first!
I carefully identified each set of 12-2 wires in the box. This can take some time with three sets of wires. One way to do this before you actually remove all the wiring from the old plug is to remove one set of hot and neutral wires at a time and tape them off with electrical tape or a wire nut and then turn the power back on and see what is still powered. If the plug you are working on no longer has power, then you just removed the Line source side. If it does still have power then you have removed one of Load sides of the circuit.
*Be careful to remove the wires in hot/neutral (black/white) pairs making sure that the pair you are disconnecting come from the same 12-2 insulated cable. Several of the duplex outlets that I have replaced in my home were originally wired such that the hot side wires and the neutral side wires were screwed into terminals in no particular order. In other words, it is very possible that the top terminals in the back or side of the outlet have a neutral and hot from different 12-2 cables. This doesn't matter with a simple duplex outlet where the outlet is just a node on each side, but it makes a big difference when wiring a GFCI.*
Because the existing outlet box could not really adequately accommodate the larger size of the GFCI and the amount of wiring including splices that had to fit behind the new GFCI, I had to remove the old box and replace it with a new larger 1-gang plastic box.
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I now added a couple of short jumpers from the to Line side of the GFCI. These will connect to the pigtail splices in the box.
Next I connected one of the grounding wires to the actual ground terminal on the GFCI. Notice that the other grounding wires are pigtailed to it further back.
Here I have screwed in the set of Load wires from the portion of the circuit I want this GFCI to protect.
Next I pigtailed the remaining hots and neutrals together respectively with a wire nut.
Use a receptacle tester to double check your wiring once the outlet is secured into the box and the power is on.
Here is the finished GFCI and wall patched with small piece of drywall and lightweight spackling.
Finally, I moved to the easier job of replacing the outdoor porch receptacle with a GFCI and new cover.
Notice this GFCI has it's Line side on the bottom terminals and the Load terminals are unused because this is conveniently the end the circuit.
This receptacle was installed in the concrete block on my back wall, so I was determined not to try to replace this older box with larger new one as I had to do in the garage. There was only one set of wires and ground coming into this box, so I was able to get the GFCI to fit.
Given the tight space, I added some electrical tape to each side of the GFCI to help prevent the possibility of the side terminals grounding to the box.
Now the cover.
Again, here is the final wiring diagram for the circuit as it is now.
